The latex aggregation method has long been used for detecting a target substance in a sample. In the latex aggregation method, in order to detect an antigen present in liquid such as a biological sample, the liquid and latex carrying the antibody or a fragment thereof that specifically binds to the target antigen are mixed, and the degree of latex aggregation is measured to detect or quantify the antigen (e.g., Patent Document 1).
According to the latex aggregation method, aggregation of latex is facilitated by an antigen, which is added as a sample and cross-links a plurality of latex-bound antibodies. This simple procedure allows for easy and rapid detection of an antigen. However, when the amount of the antigen is small, since it is difficult to generate cross-linking, a sufficient amount of latex cannot aggregate. Therefore, it was difficult to detect a small amount of antigen.
Thus, methods utilizing an enzyme-substrate reaction, such as ELISA and CLEIA, are widely adopted. In these methods, for example, a primary antibody that specifically to an antigen is bound to an antigen, and a secondary antibody having an enzyme is bound to this primary antibody. Then, an enzyme substrate is added and the reactivity of enzyme catalysis is measured to detect or quantify an antigen.
According to these methods, by using a luminescent reagent as a substrate for example, the high detectability of a luminous reaction after adding the substrate allows detection of a small amount of antigen.
Patent Document 1: Japanese Examined Application Publication No. 58-11575